1. Field of the Invention
The present invention relates to processing signals. More particularly, the present invention relates to a system and method for processing signals pertaining to a filtering system or digital microphone decimation filter.
2. Description of the Related Art
Digital microphones accept a square wave clock at 64 times the ultimate sample rate of their audio signal, and return a stereo bitstream at that clock rate. The bitstream is the output of a 4th order sigma-delta modulator. The task of a digital microphone interface is to filter the out-of-band noise from this bitstream and decimate it to the audio rate.
In other words, a digital microphone interface accepts a bitstream at 64 times the output sample rate, and decimates it with filtering to the output sample rate to provide the output digital audio stream as a series of samples. As shown by Dattorro et al. (U.S. Pat. No. 5,027,306, filed May 12, 1989, entitled “Decimation Filter As For A Sigma-Delta Analog-to-Digital Converter”), which contents are incorporated by reference in their entirety herein, this can be done by brute force using a single FIR filter. For 16 bit quality, they show this filter to be of approx order 2048 (symmetric: 4096).
What is desired is a more efficient and improved digital microphone decimation filter architecture system and method for processing signals thereof.